Process of forming joints.



W. A. DARRAH.

PROCESS 0F FORMING JOINTS.

APPLICATION FILED JULYzz, 1911.

Patented man1?, 19141.

Y 'y ISI WILLIAM AUSTIN DARRAII, orLBRooKLYN, NEW Yonu.

PROCESS 0F FORMING J' OINTS.

Specification of Letters Patent.

Patented Mar. 17, 1914.

Application led July 22, 1911. Serial No. 640,021.

To all lwhom t may concern? Be it known that I, WILLIAM AUSTIN DAR- RAH, la citizen of the 'United States, and a resident of Brooklyn, in the county of Kings and State of New York, have invented a certain new and useful Process of Forming Joints, of which the following is a specification.

My invention relates totight joints beitween glass, silicates, quartz, porcelain, and similar insulators, and a conductor; and this specicationdescrbes the methods of const-ructing such joints, 4and thedetails and,

'structure of the joints vvhenmade.A

The obj ect of my invention is to provide a joint between a conductor and glass, quartz,

porcelain, or the various silicates, and other. insulators which may be used 1n the arts as a glass tube is reasonably tight, yet it is com-v paratively very expensive due principally to the high price of metallic platinum. Such a oint also requires considerable skill in construction where the diameter of the platinum is large or when the parts connected to the platinum lhave a large capacity for conducting or for radiating heat, or when it is not convenient to maintain the platinum at a white heat.- Moreover a platinum seal is not absolutely permanent, even when constructed under the most favorable conditions, as is demonstrated by the gradual deterioration of mercury vapor lamps and rectifiers, which when heated, or when alternately heated and cooled as a result ofservice conditions exhibitl a progressive leaka e of air into the exhausted chamber, a consi erable portion of this leakage taking place along the seal. This failure of platinum seals is due to a number of causes butresults largely from the high temperature necessary for making the joint, and from the difference in the thermal coetlicient. of expansion of glass and platinum. Thus, because of the high cost of commercial process, the glass surrounds the latinum, instead of the platinum surrounding the glass, and the result 1s that as the platinum is sealed into the glass at a high platinum, in the commonn temperature, and as it dontracts more rap# idly than most kinds of glass on cooling, the

. glass is placed under tension which is a condition it is poorly adapted to stand. The forces thus created-tend to gradually separate the platinum from the glass thus eventually causing theseal to fail. This is especially truc of such types of apparatus as mercury lamps and mercury rectitiers, ctc.,

which are normally operated at rather high l temperatures, especially if overloaded.

`To overcome the defects' outlined above, and to avoid the expenseof 'the large qifantity of platinum which has been necessary are the objects of my`invention. These objects may be accomplished in the following man ner 1. By employing a certain design of joint as set forth. 2. By employing certain materials and combination of materials in -the construction o-f the joint. 3. By employing certain processes in constructing the joint. A description of these means which comprise my inventionis given in this specir-fication land then definitely pointed out in the following claims.

VConsidering rst the form of joint it is a well known fact that the elastic limit of glass and the insulators under discussion, is

much greater for forces which produce compression than for forces which produce tension. It therefore follows that glass'and insulators such asquartz, porcelain, silicates, hard rubber, bakelite, etc., which also pos Sess this property2 will stand a much greater force in compression than in tension and the first part of my invention consists in so designing a joint between the materials in question, and a conductor, such that all or the larger part at least of the strains will be in compression. The strains here referred to include those normally resulting from the diiferent thermal coefficients of Xpansion of the two materials, when subjecte to temperatuie' variations.

Referring now to the drawing, Figures 1, 2, 3, and 4 are sectional views indicating some of the various forms in which m invention may be applied, though it is evident that there are many other forms which come underthe spirit of this specification. The joints which are shown in Figs.v 1, 2, and, are specially applicable to tubes or surfaces having relatively small radii of curvature, while the form shown inFig. Il, may be applied to a surface with a larger radius of curvature or to a flat surface. Fig. 5 is a ing layer which maybe formed by any of' the methods later to be described in this specification, or by other methods.

3 and 3Il indicate the conductor which is joined to the insulator l, while 4C indicates a conductor which may be employed in some cases to close the opening in the tube or' plate l, while theconductor 3 is being put into place. Thus 4 maybe a solid conductor as lead, solder, or graphite, over which the conducting layer 3 is electrodeposited, or 'otherwise added, or 4 may be a mercury globule, or other liquid conductor. In either case it may or may not be removed after 3 is added.

I desire it to be clearly understood that the actual types here shown are merely a few illustrations of the many modifications possible, and which come under the scope of this invention. I further desire it to be understood that where an insulator is mentioned, in `this specification, that the term is used to include glass, silicates, quartz, porcelain, bakelite, hard rubber and various composition materials and the .large class of allied substances, such as hard rubber, bakelite,

i compositions, etc., having somewhat similar properties. It is in this sense that the term insulator is used in the specification and in the claims.

Now it may be assumed that in ordinary service conditions the range of temperatures which is encountered is included between the limits of -1()o C. and +2000 C., this being merely an assumption and not having any bearing whatever on the process or the range to which it is applicable, so that if a conductor (Fig. l) 3, is used, having a thermal cocllicicnt ol expansion greater than that of glass, or the insulator in question, (1),'and

if it. be formed around the tube 1, while both the insulator` and the conductor are at a temperature greater than +2000 C., then at this temperatureand all others lower than this, and thus within the working range previously defined, the conductor 3, will exert a compressive force upon the tube or insulator 1, due to the fact that the conductor tends to contract more rapidly than the insulator. If on the other hand, a conducto-r is employed, the thermal coellicicnt of expansion of, which is not greater than that of the insulatorand if it be brought into very intimate lcontact with the outside oi' the tube or insulator while at a temperature lower than -100 C., on raislng the temperature to'any tween the conducting `cap and the insulator I at a relatively high temperature if the conductor has a larger coefficient of expansion than the insulator.`

' For obvious reasons it is advisable to use materials which differ but, little in thermal coeticient of expansion from the] insulator, i

since if this is done the st-rains resulting from changes of temperature are kept a minimum. On the other hand it isl impracticable to employ conducting materials` which have Iexactly the same coeficientbf expansion as the insulator, both because of the expense of the metal and the variations which commercial conditions introduce in the manufacture of the insulator and in the conductor. I have found it advisable therefore to choose such a. conductor, that allowing for commercial variations of both materials involved, the thermal coelicient of expansion of the conductor-'is certain to be consistently greater or less than that of the insulator. Because of the greater ease of securing commercial materials I have found it more satisfactory to use a conductor having a greater' thermal coefficient of eXpan-' sion than that of most glasses or insulators, but I do not desire tolimit myself to this choice.

It is Well known that iron and certain iron alloys may be obtained, with a coelicient of expansion less, equal or greater, than that of glass and insulators generally, accord-ing to the composition of the alloy. Thus iron and steel having aismall percentage of nickel, or steel containing a small percentage of copper and manganese, as well as commercially pure iron are materials well adapted for use in the conducting portion of the joint. Thus the so-called nickel steel containing 20% of nickel has a thermal coeflicient. of expansion of approximately 0.000011 against 000000883 for an average glass. Similarly a 30% nickel steel gives a coetlicient of expansion of 0.0000077, and 50% nickel steel, a value of .00000992 Also a steel orcommercially pure iron containing .39% copper and .89% manganese gives a eocflicient of expansion of 0.000010. Further, under some conditions, bismuth may have values of 0.00001310 and antimony 0.000010.

I do not desire to limit my invention to posited any of the conductors described above, as

these and many other lmetals and alloys may sometimes be used, according to the conditions. In the description which follows iron will be mentioned-asv an example but the processes are applicable to other metals or alloys by making such modicatlons as one skilled in the art can readily devise.

Having .now described the structure and the materials employed in making a tight lioint between a. conductor and `glass, quartz, silicates. porcelain, hard rubber, bakelite, and the like, I will now disclose the process of construct-ing such a joint. This process consists of lirst rendering the surface of the insulator conducting and secondly of depositing a layer of metal upon the conducting surface thus forme-d. The formation of the conducting layer can be brought about by electrolytic or by thermal methods as will be described. One method of rendering the surface of the glass, quartz,et.c., conducting consists in dipping` the insulator in question into a. solution of lplatinum in aqua regia. or into a solution of chloroplat-inic acidfand then heating the insulator gradually until the vliquid is evaporated. thus leaving a deposit .of platinum salts upon the surface of the insulator. If now the temperature of the tube be still further raised,A

the platinum salts will vbe decomposed, linelv divided metallic platinum being dein accordance with well known formula. This layer is indicate-d by reference number 2, in the drawings. The temperature should then be still further increased until the surface of the tube orinsulator is softened somewhat, thus allowing the finely divided metal to be fused into the insulator, thus forming the layer 2, of the figures.

The process described above should be repeated sufficiently to secure auniform deposit of the requisite density and continuity for the successful operation of the following steps. i

Instead of the method described above, an electric arc formed between platinum electrodes in air, or in case a direct current is employed one platinum and one electrode of another metal or conductor may be used.

In this case the direction of the current should be such that the vapor of the are is supplied from the platinum electrode. The insulator to be treated should then be previously heated tol avoid strains resulting from sudden heating and cooling', and then lit should be passedthrough the arc in such a man ner that the vapor will be condensed upon its surface. A high tension arc is preferable for this purpose since it makes possible aI longer vapor column thus allowing av greater separation between the electrodes; A

In addition to platinum I have found that iron may be used for the arc terminals provided the are and insulator be maintained in a reducing or` inert atmosphere. Also the metals palladium, gold, arsenic, antimony, silver, etc., may be used in an inert atmosphere, though none of/these appear to be asf satisfactory as platinum.

Another methodof rendering the insulator conduct-ing, consists in raising the temperature of its surface to the point where eleetrolytic conduction takes place. This maybe done by a suitable electric 9heater within or around the tube, or the insulatormay be inserted in a flame.

There are other methods of rendering thesurface of the insulator conducting, such as the deposition of an antimony, a copper, an arsenic, or a silver mirror upon the surface, either from liquid solutions of the salts of these elements 'or from gaseous compounds or from vapors. Vhichevermethod is employed the insulator should subsequently be heated until the metal is melted into the surface. This should be done in an inert atmosphere. I also desire to include among the processes of ,rendering the surface of the insulator conducting, the methods which comprise a reduction of the compound of which the insulator is composed andgalso methods which depend for their effect upon the carbonization or decomposition of the material. of the insulator. Thus, as eX- amples of reduction of the surface, the insulator may be subjected to the effects of X- rays, cathode or vacuum tube-discharge, to .the radiations. of radioactive material, to light of short Wave lengths, to electrolytic action, etc. An example of the carbonization or decomposition of an insulator is found in the heating of hard rubber, bakelite, etc., to suitable temperatures.

Considering now the process of forming the conducting layer 3,'upon the insulator, I

have found that electrolytic methods arel most satisfactory though thermal and other methods may be employed. By thermal methods I referto the casting or welding of the conductor 3, to the conducting surface of the insulator or the metallic deposit thereon.

The electrolytic deposition of iron, iron lalloys or other metals or conducting materials may take place from most of the well known bat-hs employed by electroplaters, the v precaution being taken howeverto maintain the said baths at the necessary temperatures to secure the results described in this specification. It will also be necessary to maintain the bath, 4the insulator, the electrodes, etc., under increased pressure in a number of cases in order to prevent excessive evaporation at the elevated temperatures which may be employed. I have found that an aqueous solution of ferrous sulfate containing a large percentage of glycerin is a satisfactory bath for temperatures of about 18.0 C., although there are of course many others equally effective. y sired to submit the finished joint to temperatures higher than can readily be 0btained in a bath containin water or `an aqueous solution, even under convenient ressures, other' solvents maybe used. Thus 1n the case of iron the melted double chlorid of iron and sodium or a mixture of ferrous and calcium chlorids or a solution of ferrous oxids in borax, and other well known compounds may be employed, according to the temperature at which it is desired to demay be one of those Well known solutions for plating this metal, as for instance a solution of tartar emeti in water and-hydrochloric acid.

' It is desirable, though not absolutely necessary that the anode or positive electrode be composed ofthe material which it is desired to plate upon the conducting surface of the insulator. In case the anode is not of the same composition as the material which it is desired to plate upon the insulator, it

l' should preferably be of some material which is not appreciably dissolved during the process of plating, and under these conditions the electrolyte should be renewed frequently to `insure that the composition of the deposit is satisfactory and that the physical characteristics of the deposit are those required.

The potential applied to produce decomposition should be adjusted to a value which will give the most suitable current density for the particular metal or alloy which is being worked. The current density is different fer each case depending upon the composition of theelectrolyte, the size and position of the electrodes, the surface exposed, etc.,.and no definite comprehensive rule may be drawn up. It may be stated however that to insure a strong, irmlyadhei-ing, gas-free deposit the current density should be kept low. My experiments have indicated that the addition of `gelatin, glue, glycerin, sugar and similar agglutinous or colloidal materials makes aliowable a much higher current density than would be possible otherwise. By the term a temperature approximately as high as any to which it will be subsequently subjected, it is intended to include a difference between the temperature of formation of the conducting layer, and the maximum subsequent tem- In case it is def what I claim and per-attire such that the strains produced by the difference in the coefficients of expansion of the insulator and the conductor will not isa variable quantity depending upon the materials employed, their coefficients of expansion, their elasticity and elastic limits, as well as the operating temperatures of the joints.

, Having now fully described my invention,

desire to secure by Letters Patent is as follows 1. The method ofjoining a conductor to an insulator, which consists in rendering the surface of the insulator conducting, and forming a conducting layer thereon, by electrodeposition at a temperature of approximately as high as any to which the joint will be subjected under conditions of treatment or operation.

2. The method of joining a conductonto an insulator by rendering the surface of the insulator conducting and electrolytically depositing thereon the said conductor while both conductor and insulator are at a tcmperatu're such that at any temperature to which they will be subjected under subsequent treatment or operation the joint will be in compression.

3. The method of making -a seal between la conductor and an insulator which consists in rendering the surface of the insulator conducting and attaching the conductor thereto by electrodeposition, at a temperature approximately as high as any to which the seal, will be subjected under subsequent treatment or operation.

4. -The method of joining an insulator to a conductor by rendering the surface of the insulator conducting and depositing the conductor thereon electrolytically, said deposition taking place from a bath, the temperature of which is approximately as high as anyto which the joint will be subjected, under subsequent conditions of manufacture or performance.

5. The method of making a seal between a conductor and an insulator which consists in rendering the surface of the insulator conducting, and attaching the conductor theretoby electrodeposition at a temperature such that the joint will be under compression at any temperature to which it will be subjected under subsequent treatment or operation.

Signed at Brooklyn, Ain the county of Kings and State of New York this 19th day of July A. D. 1911.

. WILLIAM AUSTIN DARRAH.

Witnesses:

FERDINAND LEE, .TUNrUs P. VANCLEAVE.

subsequent 

